Addressing multicast group integrity management with particular regard to policy specification, this paper discusses our approach referred to as MGMS/GML - a tailored Multicast Group Management System complemented by our Group Management Language. We classify and compare existing policy specification approaches and find that none is sufficiently suitable for our problem domain, which includes tasks such as specifying and controlling integrity conditions on multicast group composition, e.g. limiting the number of senders in a group, or placing a cap on member fluctuation. Typical problems in group integrity management are identified, and an example illustrates the use of GML. Following an architectural and functional overview of our system, we look at selected implementation issues and describe how policies may be specified at runtime.